The invention relates to a device for converting energy of an exhaust gas to torque input to a crankshaft of an engine, such as an internal combustion engine. More particularly the present invention relates to improvements of the design and control of such turbocompound devices.
The invention can be applied in heavy-duty vehicles, such as trucks, buses and construction equipment. Although the invention will be described with respect to a truck, the invention is not restricted to this particular vehicle, but may also be used in other applications turbocompound devices such as aero or marine systems.
A turbocompound unit is a vehicle component used for recovering a part of the energy of the exhaust gas flow and to convert that energy into a rotational movement of a shaft. The rotational movement of the shaft is transferred as a torque increase to the crankshaft of the engine of the vehicle. Normally, the turbocompound unit has a shaft wherein a turbine wheel is arranged at one distal end. When the internal combustion engine is running exhaust gas will flow into the turbocompound unit and cause the turbine wheel to rotate. Hence, the shaft of the turbocompound unit will rotate accordingly. The opposite end of the shaft is provided with a gear wheel which meshes with additional gears for causing a rotational connection between the shaft and the crankshaft. When the shaft is rotating due to exhaust gas flowing through the turbocompound unit, the rotational energy of the shaft will be transferred to the crankshaft as a torque increase.
The use of turbocompound units has proven to provide significant advantages on driving economics as well as on the environment; the energy recovery from the exhaust gas flow will fact reduce the fuel consumption of the vehicle.
US2009/0139231 describes a turbocompound unit for which the rotational energy of the turbine wheel is transmitted to the crankshaft via a hydrodynamic clutch and a freewheel. The freewheel is integrated into the power transmission path between the turbine and the crankshaft of the engine for disconnecting the turbine form the engine when the turbine speed is lower than the comparable engine speed. The hydrodynamic clutch is provided for reducing rotational oscillations from the crankshaft.
Although the turbocompound unit prevents the turbine from being driven by the engine there is a risk that rotational parts of the turbocompound unit are subjected to overspeed, for example in case of wrong gear shift. Since this may lead to damage and malfunction there is a need for an improved solution allowing for control of the rotational speed of the turbine, not only by allowing the turbine to freewheel.
It is desirable to provide a turbocompound unit overcoming the above mentioned drawbacks of prior art units.
By the provision of a turbocompound unit which comprises brake means, it is possible to control the rotational speed of the critical components of the turbocompound unit, such as the turbine, actively.
According to an embodiment the means configured to operatively connect the turbine arrangement to the crankshaft comprises a gearing. The gearing may comprise at least one gear having teeth for meshing with a corresponding gear of the crankshaft, and wherein the freewheeling means is provided as, a freewheel clutch being arranged radially inside said teeth. Hereby an advantage is provided by the fact that the freewheel clutch does not require additional space, but may be incorporated in already present components of the turbocompound unit.
In an embodiment the brake means comprises a disc clutch. The disc clutch may be provided at one end of a shaft, and the freewheel clutch may be arranged onto the same shaft. This is advantageous in that the shaft may be provided adjacent to the crankshaft such that the freewheel clutch and the brake means are affecting the operation of the majority of the rotating parts of the turbocompound unit.
In one embodiment the freewheel clutch is arranged adjacent to said disc clutch whereby the freewheel clutch and the disc clutch may be subject to service without dismounting the gear.
In another embodiment the freewheel clutch and the disc clutch are arranged at opposite ends of the shaft, whereby space normally available at the turbine side of the shaft may be used for accommodating the disc clutch.
In an embodiment the disc clutch is hydraulically actuated by means of a piston. This is advantageous in that efficient actuation is provided, allowing for rapid response and accurate torque control.
In an embodiment the shaft comprises an oil conduit for providing lubricating fluid to the freewheel clutch and/or the disc package. Hence, the interior space of the shaft may be used for forming a lubrication conduit without requiring additional space.
In an embodiment the freewheeling means and the brake means are provided by means of a clutch having a connection mode for engaging the turbine arrangement with the crankshaft, a freewheeling mode for disconnecting the turbine arrangement from the crankshaft, and a braking mode for braking the turbine arrangement relative the crankshaft. Hence a less complex solution is realized by incorporating, the freewheel and the brake means in a solitary device.
In an embodiment the turbocompound unit further comprises a controller having at least one input for receiving a signal representing the operational status of the turbocompound unit, a determination unit being configured to determine a desired operational status of the turbocompound unit and to calculate a corresponding control signal, and at least one output for transmitting the control signal to the brake means and/or to the freewheeling means. It is thus possible to actively control the operation of the turbocompound unit for optimal performance.
In an embodiment the input of the controller is configured to receive a signal representing, the engine torque and the engine speed of the associated internal combustion engine, and wherein the determination unit is configured to determine a risk of oil leakage in the turbine arrangement. Such embodiment is advantageous in that it could remove the need for a buffer air system which otherwise is necessary in order to prevent oil leakage into the exhaust gas path of the turbocompound unit.
In an embodiment the input of the controller is configured to receive a signal representing the rotational speed of the turbine arrangement, and wherein the determination unit is configured to determine a risk of malfunction due to engine overspeed. This is advantageous in that brake means may be activated for preventing malfunction.
In an embodiment the input of the controller is configured to receive a signal representing the current driving mode, and the determination unit is configured to determine a risk of excessive friction of the turbocompound unit, i.e. when net output torque from the turbocompound unit to the engine is zero or below zero.
In another embodiment the input of the controller is configured to receive a signal representing start-up of the internal combustion engine, and wherein the determination unit is configured to determine a risk of excessive load on an associated starter.
Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.
The invention also relates to an internal combustion engine system comprising an internal combustion engine having a crankshaft and a turbocompound unit, as well as to a vehicle comprising a turbocompound unit.